1. Field of the Invention
The present invention relates to color system conversion processing and generation of a color matching table.
2. Description of the Related Art
When performing color matching between different imaging equipments such as a monitor and printer, it is generally impossible to match the spectral characteristics of both the imaging equipments, and color matching using metamerism is used. Metamerism is a method of matching colors perceived by the humans based on the so-called Young-Helmholtz's trichromatic theory in which when the human perceives the color, he/she perceives the color based on responses of three kinds of cells called cones instead of perceiving the spectral characteristic itself.
As conversion from spectral data into trichromatic data, that is, color system conversion processing, for example, a method of converting data into XYZ tristimulus values using color matching functions (CIE 1931 color matching functions) is used. The color matching functions were defined by CIE (Commission Internationale de l'Éclairage) in 1931, and have become widespread.
It has been pointed out, however, that the CIE 1931 color matching functions cause an error with respect to the actual visual characteristic. For example, the CIE 1931 color matching functions are defined by the average value of results of performing a color matching experiment by a plurality of examinees. However, it is known that the color matching functions have individual differences.
Japanese Patent Laid-Open No. 2010-169427 discloses a technique associated with a color system conversion method considering the individual differences of the color matching functions. Literature 1 below describes that even for the same observer, color matching functions to be derived are different due to a difference in color matching experiment method for deriving color matching functions.
Literature 1: Yasushi Kita, et al. “Discrepancies between Color Appearance and Measured Chromaticity Coordinates of High Intensity Discharge Lamp and White LED”, Journal of the Illuminating Engineering Institute of Japan Vol. 94, No. 2, p. 92, February 2010.
However, it is known that color matching functions change depending on a person, and also change depending on a target color even for the same observer. FIG. 1 shows the schematic arrangement of a color matching experiment for obtaining color matching functions. As the color matching experiment, there exist a maximum saturation method (MSM) which uses, as a test stimulus, light obtained by synthesizing a plurality of high-saturation monochromatic light beams (for example, bright line spectra of 435.8 nm, 546.1 nm, and 700 nm), and a Maxwell method (MWM) which uses a single white light beam as a test stimulus. However, color matching functions to be derived by the test stimuli are different.
In color system conversion processing using identical color matching functions, it is impossible to obtain sufficient conversion accuracy depending on a target color, thereby deteriorating the color matching accuracy.